Add CMS Management Functionality

- Introduced a new CMS management feature, including the ability to create, retrieve, update, search, and delete CMS entries.
- Implemented the CMS entity, repository, service, and handler layers following Clean Architecture principles.
- Added API endpoints for CMS operations in Swagger documentation, ensuring comprehensive API specifications.
- Enhanced error handling and validation for CMS data, improving robustness and user experience.
- Updated the main application to initialize the CMS repository and service, integrating them into the existing system.

internal/cms/errors.go

@@ -0,0 +1,13 @@
+package cms
+
+import "errors"
+
+// Custom errors for cms domain
+var (
+	ErrCMSNotFound        = errors.New("cms not found")
+	ErrCMSKeyRequired     = errors.New("cms key is required")
+	ErrCMSKeyExists       = errors.New("cms with this key already exists")
+	ErrInvalidCMSData     = errors.New("invalid cms data")
+	ErrUnauthorizedAccess = errors.New("unauthorized access to cms")
+	ErrInvalidKeyFormat   = errors.New("invalid cms key format")
+)